hi! fractions are as in the name, a fraction of a number. to find the one above you would have to make the denominator or bottom number the same as the other fractions denominator. to find this, make the bottom numbers equal.
4 can be multiplied by 3 to get to 12, and so whenever you multiply the bottom number you need to multiply the top, so now 1*3.
It would be 3/12+ 5/12 now , or 8/12.
Sometimes they like you to make it the smallest possible so just divide the top number and the bottom number by the same number such as 4 for this case. Now the number would be 2/3 because 2*4 is 8 and 3*4 is 12. Does this make any sense?